The distribution of transposable elements (copia, 412 and 297) were surveyed by in situ hybridization to 20 independent wild caught X chromosomes. The frequencies of various sites indicated that no site is commonly occupied. A theoretical model of the evolution of transposable elements in Mendelian populations was put forward. The analysis suggested that the distribution found in the X chromosomes is consistent with average number of transpositions per copy in the species as a whole being greater than 50.